"Thick" (&lt;50 nm) epitaxial layers have been grown on nonplanar substrates by various growth techniques, e.g., liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), and organometallic chemical vapor deposition (OMCVD). In all cases, the nonplanarity of the substrate gives rise to lateral thickness variations in the epitaxial layers. Such laterally patterned structures have been useful for optical wave guiding.
Ultra-thin (&gt;50 nm) epitaxial layers have also been grown on planar substrates. For such thin layers i.e., layers whose thickness is comparable to the deBroglie wavelength of charge carriers) quantum size effects in one dimension (along the growth direction) modify the material properties (e.g., bandgap and refractive index). Hence, by tailoring the thickness of the epitaxial layers, it has been possible to vary the resulting superlattice (or quantum well) material properties. For example, selection of the suprlattice (SL) periodicity results in selection of the material bandgap. In addition, these superlattices give rise to new features, e.g., enhanced nonlinear optical properties. Furthermore, it has been shown that the SL period (or layer thicknesses) in the direction of layer growth, allows one to fabricate structured materials in which the physical properties in the direction normal to the substrate plane differ based upon the SL period. Devices which rely not only upon the new properties of the SL materials, but also on quantum size effects that occur in the individual layers, have also been demonstrated, e.g., quantum well lasers, resonant tunneling devices, quantum-confined Stark effect modulators, etc.
In U.S. patent application Ser. No. 323,402, filed Mar. 14, 1989, for E. Kapon, entitled "Semiconductor Superlattice Heterostructures on NonPlanar Substrates" and assigned to the same assignee as this application, there is disclosed a method of forming thin (&gt;50 nm) epitaxially grown semiconductor layers having a superlattice with laterally varying periodicity grown on a nonplanar e.g., grooved substrate. The layers vary in thickness and, hence, physical properties laterally along the substrate plane.
The production of optical waveguides with low propagation losses and optical waveguide structures with improved design for Y-junctions and interconnection is still sought after in the art.